Features of formation of surface layers in steel VKS-10 (13Kh3N3M2VFB-Sh) under thermal and thermochemical treatments, i.e., laser processing with and without surface fusion and subsequent vacuum nitriding, are considered. The effect of preliminary laser treatment on the kinetics of saturation of the surface with nitrogen is studied. It is shown that the preliminary laser treatment without fusion of the surface followed by nitriding provides a higher effective thickness of the layer on steel VKS-10 and higher wear resistance of the surface than the treatment with fusion.

We consider the motion of a classical electron in the field of a monochromatic plane wave of an arbitrary (linear, circular, or elliptic) polarization in an arbitrary inertial reference system. It is shown that the ratio of the energy emitted by an electron moving with acceleration in the field of the wave during the time equal to its period to the mean energy of the oscillatory motion of the electron can be expressed in terms of two dimensionless relativistic invariant parameters. As the criterion determining the applicability limit of the approximation presuming a small influence of the radiation damping on the motion of the classical electron in the field of the monochromatic plane wave, we consider the condition of equality of energy emitted by the electron during the period and the mean energy of the oscillatory motion. The applicability boundary of the approximation is constructed in the space of two dimensionless invariant parameters. In the reference system in which the electron has been at rest prior to the arrival of a wave with a sharp leading edge, one of these parameters is proportional to the frequency of the incident wave, while the other, to its intensity.

Laser surface modification of steel with tungsten carbide (WC) particles provides significant wear-resistance increasing. At the same time, it is important to achieve a uniform distribution of reinforcing particles over the depth of the created composite layer. To find out the possibility of the particles of different sizes application and to determine the allowable ranges of parameters of the coaxial to the laser beam powder injection, the calculations of the kinetics of penetration of WC particles into the molten surface of a sample made of carbon steel were carried out. It was shown that WC spherical particles with a diameter of about 50–150 µm, which are the most suitable for this application, could be injected into the entire depth of the molten part of the steel matrix if their speed of movement from the nozzle edge is from 6 m/s. All of them must reach the boundaries of the molten pool, and its shape determines their distribution throughout the depth. This provides the possibility to achieve uniform hardening throughout the depth by varying the parameters of laser radiation.

ABSTRACT Formation, structure and properties of welded joints in cryogenic austenitic nitrogen containing steel of chromium – nickel – manganese – nitrogen alloying system with reduced nickel content are investigated. Under optimal laser welding conditions, a weld of small width with almost parallel walls is formed. This helps to reduce residual stresses and strains. There is a significant reduction in the structure size parameters of the weld compared to arc welding. The mechanical properties of laser welds are within acceptable limits, so the tensile strength is 0.84–0.96 of the base metal. Fractographic analysis of the fracture surface of welded samples after testing showed the presence of developed zones of plastic deformation, which characterizes the laser-welded joint as highly plastic.

Pulse laser welding provides welds in thin-walled and miniature structures without their significant deformation. However, the features of the weldment surface geometry are the foundation of the presence of corrosion and stress concentrators. To eliminate them and to decrease the weldment surface roughness pulse laser processing with surface melting is often used, however, the influence of this process on the weldment properties is not sufficiently studied yet. In this work it is shown that pulse laser processing with the weldment surface melting with the optimal regime parameters provides the decrease of the its roughness more than twice and the elimination of the corrosion and stress concentrators. The process can be carried out on the same equipment with the welding. Wherein, mechanical properties of the welds are practically unchanged, and no significant changes of the metal structure were founded. The tendency of the welds to corrosion cracking as a result of the applied processing, at least, does not increase.

ABSTRACT The possibility of application of laser carbon steel for railway transport wheels manufacturing surface alloying with spherical tungsten carbides WC was considered. Experiments showed that volume part of reinforcing particles could reach 58% when laser powder alloying is applied. In the same time, if volume par of WC exceeds 16%, cracks on the surface are observed.

Among the methods of additive technologies, coaxial laser melting, i.e. direct metal deposition (DMD), is quite widespread. Essentially, this process is about creating objects by sequentially deposing layers of powder and melting them due to their simultaneous supply through a nozzle with focusing of laser radiation into the processing zone. Various powders are used as materials for this technology, the powders being selected depending on the tasks and final characteristics. One of the promising directions for implementation is the creation of complex structures from copper alloys for aircraft construction. Despite the fairly widespread use of this technology in relation to copper alloys, in particular bronzes, there is a small amount of data and research for this technology. The purpose of this study was to understand the process of forming the materials when grown by the DMD method. For this purpose, the fusion of bronzes with a steel substrate was investigated; special aspects were revealed, which made it possible to pose the second task - the study of fusion of bronzes with a copper substrate. As a result, the microstructure of the samples was considered and their micro-hardness was measured.

We have studied the periodical-in-voltage oscillations in the current-voltage characteristics of GaAs/AlAs double barrier resonant tunneling diode terahertz detectors. The found oscillations of the negative differential conductance are attributed to LO-phonon-branch polariton excitations stimulated by electrons tunneling through the quantum active region in the resonance nanostructure. It is argued that, due to the conduction-band profiles disposition in a manner of the inversion-like nonequilibrium cascade, the tunneling current supplies the inevitable excessive energy. The RTD serves as an internal amplifier of weak electromagnetic signals, provided by the region of negative differential conductance.

Формирование поверхностных металлокерамических композитных слоев позволяет значительно повысить износостойкость. Для этого может быть использован процесс лазерно-­порошковой обработки. При подаче порошка соосно лазерному лучу можно добиться формирования глубокого упрочненного слоя, однако при выборе параметров обработки следует учитывать снижение интенсивности луча при прохождении потока порошка и нагрев частиц в полете через облучаемую область. Расчеты показали, что при реализуемых на практике параметрах обработки снижение интенсивности лазерного излучения на поверхности детали может достигать 10%. Состояние частиц, попадающих в жидкую сталь, зависит от их размера. Частицы сравнительно небольших размеров могут испытывать оплавление, в результате интенсифицируется диффузия вольфрама в сталь.

We derive general frequency dependencies of the surface impedance modulus for conductors without the dc dissipation, i. e. for superconductors or perfect conductors. The frequency-dependent surface impedance was applied for the solutions corresponding to the spatially dispersive eigenvalues of the permittivity operator for conductors. We demonstrate that appropriately taken into account effects of the spatial dispersion can give the general frequency dependence of the surface impedance for the obtained solutions including that for superconductor. It is shown that an incorporation of the spatial dispersion leads to an appearance of the Meissner effect in perfect conductors in the same manner as in superconductors.

We derive general frequency dependencies of the surface impedance modulus for conductors without the dc dissipation, i. e. for superconductors or perfect conductors. The frequency-dependent surface impedance was applied for the solutions corresponding to the spatially dispersive eigenvalues of the permittivity operator for conductors. We demonstrate that appropriately taken into account effects of the spatial dispersion can give the general frequency dependence of the surface impedance for the obtained solutions including that for superconductor. It is shown that an incorporation of the spatial dispersion leads to an appearance of the Meissner effect in perfect conductors in the same manner as in superconductors.

Abstract The dimensions and shape of a weld pool have a strong effect on both the technological and service parameters of welded joints. To investigate the shape and dimensions of a weld pool, a device for removing molten metal from the pool cavity for different materials and thickness of the welded specimens was designed and constructed. Investigation of the shape of the pool in laser welding showed special features of the pool in comparison with arc welding

It is shown that in welding large structures with stable austenitic welding materials made of nitrogen-containing cryogenic chromium–nickel–manganese austenitic steels, cracks can form in the welded joint both during crystallization and in the solid-state at subsolidus temperatures. In laser welding, the structure of the cast weld metal can be greatly refined in comparison with arc welding and this should increase the solidification cracking resistance. In addition, laser welding can be used to produce the welded joint in a single pass thus preventing reheat cracking.

An approach to the solution of the relativistic problem of the motion of a classical charged particle in the field of a monochromatic plane wave with an arbitrary polarization (linear, circular, or elliptic) is proposed. It is based on the analysis of the 4-vector equation of motion of the charged particle together with the 4-vector and tensor equations for the components of the electromagnetic field tensor of a monochromatic plane wave. This approach provides analytical expressions for the time-averaged square of the 4-acceleration of the charge, as well as for the averaged values of any quantities periodic in the time of the reference frame. Expressions for the integral power of scattered radiation, which is proportional to the time-averaged square of the 4-acceleration of the charge, and for the integral scattering cross section, which is the ratio of the power of scattered radiation to the intensity of incident radiation, are obtained for an arbitrary inertial reference frame. An expression for the scattering cross section, which coincides with the known results at the circular and linear polarizations of the incident waves and describes the case of elliptic polarization of the incident wave, is obtained for the reference frame where the charged particle is on average at rest. An expression for the scattering cross section including relativistic effects and the nonzero drift velocity of a particle in this system is obtained for the laboratory reference frame, where the initial velocity of the charged particle is zero. In the case of the circular polarization of the incident wave, the scattering cross section in the laboratory frame is equal to the Thompson cross section.

An operator of the permittivity can completely describe alone a microwave response of conductors with the spatial dispersion. A wave problem is formulated to search the eigenvalues of the permittivity operator, similar to the problem of the wave propagation in hollow waveguides and resonators, but non-self conjugated. Dispersion relations and general solutions are obtained. A significant role of the spatial-type force resonances is considered. Due to the self-consistency of a kinetics problem, the spatial-type force resonances are added to and usually dominate over the influence of boundary conditions. The obtained resonances include particular solutions corresponding to the surface impedances for the anomalous skin effect, for superconductors, as well as four novel solutions. The general frequency dependence of the surface impedance is derived for all solutions except that for a superconductor.

The periodical-in-voltage features of the negative differential conductance (NDC) region in the current-voltage characteristics of a high-quality GaAs/AlAs terahertz resonant-tunneling diode have been detected. The found oscillations are considered taking account of the LO-phonon excitation stimulated by tunneling of electrons through the quantum active region in the resonance nanostructure where an undoped quantum well layer is sandwiched between two undoped barrier layers. Rearrangements in the I-V characteristics of the resonant-tunneling diode as a consequence of the topological transformation of a measurement circuit from the circuit with the series resistance Rs to the circuit with the shunt Rp have been experimentally studied and analyzed. The revealed substantial changes in the current-voltage characteristics of the resonant-tunneling diode are discussed schematically using Kirchhoff's voltage law.

An operator of the permittivity can completely describe alone a microwave response of conductors with the spatial dispersion. An eigenvalue problem for the nonself-adjoint permittivity operator epsilon(a) was considered generally to search the wave solutions for conductors and superconductors. An appearance of additional solutions (additional waves) due to the spatial dispersion can strongly influence the properties of nanoelectronic devices or novel superconducting materials in the form of anomalous losses for example, and should be accounted in simulation and modeling of micro- and nanoelectronic devices. It was concluded that the modulus |Z| of the surface impedance is proportional to the degree of frequency omega 2/3 for all normal conductor solutions except that for the superconductor. There was some criticism related to the idea that the electrodynamics of superconductors should be in principle reduced to those for conductors as the temperature approaches and beyond the critical temperature. We demonstrate that appropriately taken into account effects of the spatial dispersion can give the general frequency dependence of the surface impedance for the obtained solutions including that for the superconductor. It is shown that an incorporation of the spatial dispersion leads to an appearance of the Meissner effect in perfect conductors in the same manner as in superconductors.